The present invention relates to a method and an apparatus for preventing wheel spin and lateral skidding of vehicles depending thereon, such as often happens when vehicles are driven on slippery and loose grounds.
Different systems have been suggested for preventing wheel spin of the driving wheels which appears when the drive force is too high for the actual ground, whereby the driving wheels start rotating with a higher peripheral speed than the speed corresponding to the movement speed of the vehicle. One such known system operates according to the principle that the peripheral speed or the rotary speed of the driving wheels is compared with the actual driving speed of the vehicle, which driving speed is for instance observed on the idle running wheels, and that the output torque of the motor is reduced when the driving wheels have a peripheral speed which is a multiple higher than that of the idle running wheels or of any other reference object indicating the running speed of the vehicle.
The Swedish patent having the laid out publication number 445.572 shows and describes a system of the above mentioned type, which is in particular adapted to internal combustion engines of the Otto type and having a fuel injection apparatus, and the system operates so that the amount of fuel supplied to one or more cylinders is reduced step by step to a level which is determined by the rate of speed difference between the driving and idle running wheels. To achieve this fuel reduction the amount of fuel supplied to some cylinders is gradually choked by means of a valve which gradually reduces the fuel to be supplied to the fuel injection valve or nozzle until the choking is complete. Thereby the actual cylinder or cylinders are supplied with a reduced amount of fuel, whereby said cylinder or cylinders consequently give a reduced contribution of torque.
This known system is disadvantageous in some respects. Firstly the system is intended for and adapted to gasoline motors having fuel injection means and it can not be utilized in Otto motors of carburettor type or in Diesel engines. Further, the gradual choking of the fuel supply to one cylinder changes the optimum relationship between fuel and air, since always the same large amount of air is supplied to the actual cylinder independently of the amount of supplied fuel. This changed optimum fuel/air relationship leads to an impaird combustion, an un-economical utilization of the fuel, a risk of overheating of a cylinder as a result of a too lean fuel mixture, a risk that the fuel mixture does not at all become ignited and that uncombusted fuel is let out in the exhaust gas system. In the long run the said known system also may adversely influence the motor since the choking of the fuel always is made for the same cylinder during the entire stepwise choking of the fuel.
A special problem appears in motors having exhaust gas cleaning means of catalyzor type in that there is a risk that the catalyst becomes burnt out if un-combusted fuel reaches the catalyst cleaner and is ignited and burns therein.